In recent years, field emission lamps have been developed for conventional incandescent light bulbs and fluorescent lights. This type of lamp, in a vacuum vessel, causes field emission of electrons to occur by applying a positive voltage to a cathode that has an electron emission source, and causes fluorescent luminescence by causing these field emitted electrons to collide with a fluorescent substance on an anode. By properly controlling the voltage of a gate electrode that is provided between the cathode and anode, high luminance emitted light can be obtained with low power consumption.
In order to drive this kind of field emission lamp, high direct-current voltage from a switching power source is necessary; for example, JP Patent Application Publication No. 2008-13917 discloses a method in which a resonance circuit, which uses the stray capacitance of a step-up transformer for raising the switched input voltage, is used to match the ON/OFF timing of the switching signal with the resonance conditions of the resonance circuit. In doing so, it is possible to improve the high-voltage conversion efficiency by eliminating loss due to the components of a power-supply circuit, and it is possible to make the device more compact and reduce cost due to simplifying the overall circuit configuration.
However, in a field emission lamp, it is impossible to avoid variation in lamp characteristics that are caused by variation in characteristics of the electron emission source and fluorescent substance, variation in the distance between electrodes due to manufacturing, and change over time. Therefore, even when attempting to drive a plurality of lamps with the same power, there is a problem in that the optimal driving conditions for each individual lamp are different.
Therefore, when using a plurality of field emission lamps for lighting and trying to obtain uniform emitted light from each lamp using the same power, conventionally it was necessary to prepare drive units for each individual lamp respectively. Consequently, this causes an increase in the overall size and cost of the driving apparatus due to the increase in circuit parts.